Double layer relaxation in colloids

The purpose of the present study is to improve our insight into the relaxation of the electrical double layer around particles in hydrophobic sols. A detailed knowledge of the relaxation mechanisms is required to explain the behaviour of sols under conditions where the double layer is perturbed. Such conditions are frequently encountered in colloid science; for instance when colloidal particles coagulate or when they are subjected to an external field as in electrokinetics.One of the appropriate electrokinetic methods to experimentally study the dynamic properties of double layers is low-frequency dielectric spectroscopy. Previous studies have shown that latices exhibit a large dielectric response. However, these results could not be quantitatively reconciled with either electrophoresis data or existing theory. To discriminate whether the disagreements were due to theoretical or experimental imperfections, dielectric data on inorganic sols were highly desirable. The major aim of this study is to provide such data and, where necessary, to improve the existing theory. The results are described and discussed in chapters 2-5.The stability of sols against coagulation is of crucial importance for their applications. In principle, hydrophobic sols are thermodynamically unstable; they tend to form aggregates due to the attractive Van der Waals forces. However, in many cases the rate of coagulation is slowed down by the presence repulsive electrostatic forces. These occur if double layers overlap.Coagulation is a dynamic process. Particles interact on a certain time scale during which the extent of double layer overlap varies. Consequently, the equilibrium double layer structure will be perturbed, inducing relaxation processes. In principle, the colloid stability depends on the relaxation time of the double layer, which may be well of the same order as the typical time scale of a particle collision. However, the knowledge about the influence of the relaxation processes on the coagulation rate was limited. Therefore, the second aim of this study is to improve that situation. We focussed our attention on those cases where the relaxation rate of the double layer is determined by the adjustment of the surface charge density, see chapter 7. Chapter 6 discusses a related topic.A short summary of the results and main conclusions of each chapter is given below.Chapter 2 gives a description of a newly constructed fourelectrode dielectric spectrometer, designed to measure the dielectric response (or complex admittance) of sols in the frequency range of approximately 500 Hz; to 500 kHz. A four-electrode design is developed to avoid problems related to electrode polarization and, at the same time, to-enable the use of an automatic frequency response analyzer. The device is suitable for fast and accurate data acquisition, the measurement of one complete spectrum taking a few minutes only. Furthermore, it is especially designed to measure frequency-difference spectra.In chapter 3 it is shown that the thin double layer theory for the electrokinetic properties of dilute colloids can be extended to include surface conduction, i.e. a conduction contribution by ions behind the plane of shear. The calculations show that the occurrence of surface conduction leads to a reduction of the electrophoretic mobility and to an increase of the static sol conductivity and the dielectric response. Moreover, it also follows from the theory that an unambiguous interpretation of only one type of experimental data, for example the electrophoretic mobility, is impossible if surface conduction occurs. To assess whether this is the case, one is bound to also measure either the static conductivity or the dielectric response of the sol. The comparison between theory and experiment has been made for literature data on latices. For polystyrene latices, the mobility and static conductivity can be well explained if surface conduction is taken into account. However, the extended theory is not able to provide a quantitative explanation of the extreme dielectric increment of latices.Chapter 4 provides experimental data on the low-frequency dielectric response of dilute aqueous hematite and silica sols of spherical particles as a function of pH, ionic strength and particle size. The pH-sensitivity of the dielectric responses of the two sols shows that this response is a function of the surface charge density. The particle size dependence of the characteristic relaxation frequency is in fair agreement with theoretical predictions. In contrast to the case of latices, the dielectric behaviour of both hematite and silica can be well explained by classical electrokinetic theory yielding reasonable values for the ξ potentials. However, these values are systematically higher than those obtained electrophoretically. This inconsistency indicates the occurrence of surface conduction within the plane of shear, a type of conduction not included into the classical theory. By using the theory as developed in chapter 3, a distinction can be made between the (mobile) counter charge within and that beyond the plane of shear. Application to the hematite and silica data shows that a large fraction of the (mobile) counter charge is located inside this plane. This fraction increases with increasing surface charge density.The experimental and theoretical framework developed in the previous chapters has been applied to a spherical coryneform bacterium suspension in Chapter 5 . According to the preliminary results, approximately 95% of the total (mobile) counter charge in the double layer of the bacterium is located behind the plane of shear, i.e. probably within the cell wall itself. Such a large surface conduction contribution inhibits the possibility to determine the ξpotential of bacteria by electrophoretic measurements only. In this respect. additional information is necessary. The present investigation shows that dielectric spectroscopy is a useful technique to obtain that information.Chapter 6 presents a model to calculate the electrostatic interaction between two colloidal spheres, accounting for their polarizabilities. Under conditions where the potential along the surface varies during interaction, for example under those as discussed in chapter 7, the polarizability of a particle affects the electrostatic repulsion. Results are presented for spheres interacting at constant surface charge density. The calculations clearly show how the electrostatic force decreases with the polarizability of the particle. The decrease becomes larger with stronger double layer overlap, whereas it is relatively insensitive to κa. This insensitivity is a consequence of tangential screening effects inside the particles. It is pointed out that for slowly coagulating sols of particles with a fixed surface charge density, the stability ratio W is sensitive to the polarizability of the particle.Transient deviations from the equilibrium surface charge density during the interaction of colloidal particles and their influence on colloid stability are discussed in chapter 7 . Such deviations cause the process of particle encounter to become a non- first-order Markov process, which complicates the analysis of colloid stability. Two methods are presented to calculate a modified colloid stability ratio, taking such deviations into account in an approximate way. These methods differ by their estimates for the time scale of the Brownian encounter and its dependence on the height of the energy barrier. Despite these differences, both methods show that double-layer dynamics can have major consequences for the stability ratio. However, the predicted dependences of the rate of slow coagulation on the particle radius of the two methods are different. This indicates that double-layer dynamics could explain the experimentally found insensitivity of the stability ratio to the particle size, provided the time scale of the encounter strongly increases with growing height of the energy barrier. However, this proviso is unlikely to be satisfied. A simple statistical analysis indicates that the time scale of any individual encounter should decrease with growing barrier height!This thesis presents experimental and theoretical work related to double layer relaxation of colloids. It is not only of academic interest but also of significant practical importance. The results provide an encouraging basis for further research in the field of electrokinetics and stability of hydrophobic colloids

Quality indicators for measuring the level of patients' involvement in the pharmaceutical care process

Patient-centred counseling is an integral part of the pharmaceutical care process. Quality in- dicators can be valuable tools to measure the level of patients’ involvement in their personal healthcare. The aim of the study was to validate two quality indicators for community pharmacy care focusing on patient involvement. As part of the EDQM Pharmaceutical Care Quality Indicators Project (Council of Europe), at least 10 patients per indicator were recruited in each community pharmacy in Serbia and Po- land. Pharmacists targeted patients aged 18-65 years starting chronic treatment (Indicator 1) and elderly patients with polymorbidity receiving at least five chronic treatment medicines (Indicator 2). Based on patients’ answers to a questionnaire, patient-pharmacist consultations took place. For Indicator 2, patients were also offered a medication review. In total, 66% of Serbian patients and 29% Polish patients, for In- dicator 1, were engaged in pharmacist-patient consultations; 96% of Serbian and 84% of Polish elderly patients subsequently participated in medication reviews. Community pharmacists can increase patients’ involvement in their own pharmaceutical care, and there is a need for such services. This study defines a pragmatic approach to encourage/support the implementation of the pharmaceutical care philosophy and working methods in European community pharmacies

Changing climate—changing pathogens: Toxoplasma gondii in North-Western Europe

In this review, we describe the effects of global climate change for one specific pathogen: the parasite Toxoplasma gondii. It is postulated that an increase of T. gondii prevalence in humans can occur in some regions of North-Western Europe as a result of changing environmental conditions. Such a change can be predicted by using Global Climate Change models. We have elaborated such a prediction for one scenario (SRES A1) by using one specific model (CCSR/NRIES) as an example. Next to environmental factors, also anthropogenic factors may contribute to increased prevalence of T. gondii in this region. In order to counter the potential severe consequences of a potential increase resulting from the combination of climatic and anthropogenic factors, there is an urgent need for the development of a human vaccine. Until a vaccine that offers complete protection is developed, the emphasis should be on treatment optimization and prevention

The Need and Potential of Biosensors to Detect Dioxins and Dioxin-Like Polychlorinated Biphenyls along the Milk, Eggs and Meat Food Chain

Dioxins and dioxin-like polychlorinated biphenyls (DL-PCBs) are hazardous toxic, ubiquitous and persistent chemical compounds, which can enter the food chain and accumulate up to higher trophic levels. Their determination requires sophisticated methods, expensive facilities and instruments, well-trained personnel and expensive chemical reagents. Ideally, real-time monitoring using rapid detection methods should be applied to detect possible contamination along the food chain in order to prevent human exposure. Sensor technology may be promising in this respect. This review gives the state of the art for detecting possible contamination with dioxins and DL-PCBs along the food chain of animal-source foods. The main detection methods applied (i.e., high resolution gas-chromatography combined with high resolution mass-spectrometry (HRGC/HRMS) and the chemical activated luciferase gene expression method (CALUX bioassay)), each have their limitations. Biosensors for detecting dioxins and related compounds, although still under development, show potential to overcome these limitations. Immunosensors and biomimetic-based biosensors potentially offer increased selectivity and sensitivity for dioxin and DL-PCB detection, while whole cell-based biosensors present interpretable biological results. The main shortcoming of current biosensors, however, is their detection level: this may be insufficient as limits for dioxins and DL-PCBs for food and feedstuffs are in pg per gram level. In addition, these contaminants are normally present in fat, a difficult matrix for biosensor detection. Therefore, simple and efficient extraction and clean-up procedures are required which may enable biosensors to detect dioxins and DL-PCBs contamination along the food chain

Inventarisatie diergeneesmiddelen gebruik in de biologische geitenhouderij

Zowel kennisinstellingen als individuele biologische bedrijven proberen onderzoek te doen naar de effectiviteit van alternatieven voor bepaalde aandoeningen in de biologische veehouderij. Op welke schaal dit binnen de bedrijven gebeurt, was tot op heden nog niet bekend en was daarom de reden voor het onderzoek, waarvan hier de rapportage voor de biologische geitenhouderij volgt. De doelstelling van het onderzoek was het inventariseren van de gezondheidsproblemen in de biologische geitenhouderij in Nederland en de wijze van behandeling van deze aandoeningen. Hiertoe werden door middel van een aselecte steekproef 25 geitenhouders tijdens een bedrijfsbezoek geënquêteerd. De belangrijkste dierziekten die op de meeste bedrijven voorkwamen waren diarree, baarmoederontsteking en klinische mastitis. Alle onderzochte geitenhouders gebruikten minimaal 1 regulier diergeneesmiddel in het onderzochte jaar (2002). Ruim 75 % van de geitenhouders gebruikt één of meerdere alternatieve middelen voor de behandeling van dierziekten bij de geiten. De reguliere en alternatieve diergeneesmiddelen worden voornamelijk curatief ingezet. De 25 geënquêteerde geitenhouders gebruikten gezamenlijk 84 verschillende reguliere diergeneesmiddelen. Deze 84 reguliere diergeneesmiddelen bestaan voor 2/3 uit een divers scala van antibiotica. Er werd weinig uniformiteit in het gebruik van de verschillend antibioticum preparaten gezien. Aangezien de geitenhouderij een relatief kleine bedrijfstak is wordt er door de pharma industrie weinig geïnvesteerd in de registratie van diergeneesmiddelen ten behoeve van de geit als doeldier. Wel zijn een aantal reguliere diergeneesmiddelen opgenomen in de een vrijstellingslijst voor de geit van het Bureau Registratie Diergeneesmiddelen (BRD). Hoewel het arsenaal aan middelen dus formeel beperkt is worden er onder de verantwoording van de dierenarts diverse middelen toegepast die niet voor de geit als doeldier zijn toegelaten. Uit het onderzoek kan geconcludeerd worden dat er weinig consensus bestaat tussen de geitenhouders/dierenartsen op het gebied van de curatieve gezondheidszorg van biologische geiten. Van een aantal van de gebruikte alternatieve geneesmiddelen is de werkzaamheid niet door wetenschappelijk onderzoek onderbouwd en is het gebruik dus in strijd met de EU regelgeving voor de biologische dierhouderi

Carbon monoxide conversion by thermophilic sulfate-reducing bacteria in pure culture and in co-culture with Carboxydothermus hydrogenoformans

Biological sulfate (SO4) reduction with carbon monoxide (CO) as electron donor was investigated. Four thermophilic SO4-reducing bacteria, Desulfotomaculum thermoacetoxidans (DSM 5813), Thermodesulfovibrio yellowstonii (ATCC 51303), Desulfotomaculum kuznetsovii (DSM 6115; VKM B-1805), and Desulfotomaculum thermobenzoicum subsp. thermosyntrophicum (DSM 14055), were studied in pure culture and in co-culture with the thermophilic carboxydotrophic bacterium Carboxydothermus hydrogenoformans (DSM 6008). D. thermoacetoxidans and T. yellowstonii were extremely sensitive to CO: their growth on pyruvate was completely inhibited at CO concentrations above 2% in the gas phase. D. kuznetsovii and D. thermobenzoicum subsp. thermosyntrophicum were less sensitive to CO. In pure culture, D. kuznetsovii and D. thermobenzoicum subsp. thermosyntrophicum were able to grow on CO as the only electron donor and, in particular in the presence of hydrogen/carbon dioxide, at CO concentrations as high as 50-70%. The latter SO4 reducers coupled CO oxidation to SO4 reduction, but a large part of the CO was converted to acetate. In co-culture with C. hydrogenoformans, D. kuznetsovii and D. thermobenzoicum subsp. thermosyntrophicum could even grow with 100% CO (P CO=120 kPa)

Iron deficiency impairs contractility of human cardiomyocytes through decreased mitochondrial function

Contains fulltext : 191557.pdf (Publisher’s version ) (Open Access

Lipoprotein Changes Following Consumption of Lutein-enriched Eggs are Associated with Enhanced Lutein Bioavailability

Abstract Lutein is concentrated in the retina and since it cannot be synthesized by the human body, its uptake depends on nutritional intake. Lutein-enriched eggs are a good lutein source, but whether changes in lipoprotein status following lutein-enriched egg consumption may affect an individual's lutein response is not yet clear. Data from three intervention trials with lutein-enriched eggs or products made from the enriched egg yolks were combined (n=294) and analyzed to investigate the dynamics of the lutein response in relation to lipoprotein levels. Cross sectional correlation was tested at baseline between lutein and lipoprotein profiles in all participants. Subsequently two groups were selected from the combined database whereby individuals receiving lutein-enriched egg yolks (n=137) were compared with controls not receiving eggs (n=117). Significant correlations between blood lutein concentrations and total cholesterol (r=0.309; p<0.001), HDL-C (r=0.246; p<0.001), LDL-C (r=0.241; p<0.001), ApoA1 (r=0.301; p<0.001), and ApoB100 (r=0.199; p<0.005) concentrations, but not with serum triglycerides were found at baseline. Following a three to twelve month intervention, blood lutein concentrations increased from 238 to 463 ng/ml (p<0.001) in the lutein group, whereas levels in controls remained unchanged. The lutein increase in the lutein-enriched egg group correlated significantly with changes in total cholesterol, HDL-C, LDL-C, ApoA1 and ApoB100 concentrations. To conclude, individuals showing the largest lipoprotein increase following egg consumption were also those with the strongest increase in blood lutein concentration. This indicates that therapies directed at altering lipoprotein levels may indirectly affect lutein bioavailability

Laboratory tests in uveitis - New developments in the analysis of local antibody production

Analysis of local intraocular antibody production is a valuable tool with which to confirm a suspected clinical diagnosis in uveitis. We have analysed paired serum and aqueous samples for the presence of specific antibodies against toxoplasma, cytomegalovirus, herpes simplex virus and varicella zoster virus. Of the patients retrospectively diagnosed as having toxoplasma chorioretinitis 75% had a positive antibody coefficient indicating specific antibody production in the eye. Local antibody production in the eye directed against CMV confirmed the suspected diagnosis of CMV retinitis in 50% of the AIDS patients investigated. So far we have not been able to demonstrate local antibody production against herpes simplex virus (26 samples tested). Two of three patients with acute retinal necrosis had a positive antibody coefficient against varicella zoster virus. Both of these patients had an even higher titer in the aqueous than in serum. Since the choice of therapy, in infectious uveitis, depends on the causative organisms, it is very important to confirm a suspected clinical diagnosis by means of aqueous humor analysi

Inorganic hydrophobic coatings: Surfaces mimicking the nature

Added value products are being developed in ceramic industry. Different optical effects as bright metallic shine or new functionalities as hydrophobicity or bactericide characteristics are the new properties searched on the tiles. In this study, we prepare glassy coatings for tiles based on copper pigment by a conventional industrial process. The obtained coatings present different aesthetical aspects, including bright metallic aspect which confers a high decorative value to the tile. Furthermore, these metallic coatings present hydrophobic properties with contact angles with water as high as 115 degrees and also bactericide characteristics. Superficial microstructure and nanoparticles were found in the bactericide-hydrophobic samples, resembling the surface of hydrophobic leaf surfaces. This structure was formed by the crystallization of CuO nanoparticles as Tenorite due to the copper saturation of the glassy matrix at the surface of the coatings